Structural evolutionary behavior of Zr-based bulk metallic glasses under thermoplastic deformation

Abstract

Zr55·7Cu22·4Al14.7Ni7.2 alloy rods with a diameter of 3 mm were prepared by copper mold suction casting. The microstructure, thermomechanical properties and high temperature plastic deformation behavior of the alloy specimens before and after uniaxial compression in supercooled liquid region (SLR) were investigated by X-ray diffractometer, scanning electron microscope, differential scanning calorimeter and microcomputer-controlled electronic universal testing machine. And the effects of different deformation conditions on the thermomechanical properties and microhardness of the specimens after high temperature deformation were analyzed. The results show that during plastic deformation in SLR, this alloy exhibits stress overshoot in the low temperature region - high strain rate conditions, exhibiting non-Newtonian fluid properties, while alloy softening occurs in the high temperature region - medium to high strain rate, showing the deformation behavior of a Newtonian fluid. The alloy crystallizes after deformation at high temperature and low strain rate (750 K, 2 × 10−4 s−1 and 760 K, 2 × 10−4 s−1∼5 × 10−4 s−1), generating dendritic τ3 phase (Zr51Cu28Al21), while still maintaining an amorphous structure in the low and medium temperature region, but this structure has part of the amorphous matrix that has been transformed into ordered clusters of atoms, and the degree of transformation increases sharply with decreasing strain rate, which in turn causes a sharp reduction in the crystallization incubation period and the exothermic enthalpy of crystallization. And the effect of high temperature deformation on the Vickers microhardness of metallic glass was analyzed.